Vitamin C has widely been incorporated into animal feeds both as a vitamin C supplement and as an antioxidant. The physiological activity of vitamin C decreases with the influence of atmosphere and moisture and by the action of light, heat and co-existing substances, such as metal ions etc. Thus, the vitaminic effectivity thereof is apt to be destroyed easily.
Under these circumstances, attempts had been made to provide a coated granular vitamin C preparation capable of preventing the activity decrease of vitamin C.
The hitherto proposed methods for preparing coated or encapsulated products of water-soluble vitamins inclusive of vitamin C can be classified into the following two generalized ways:
The first way comprises the steps of preparing an oil suspension of a particulate product of a water-soluble vitamin in a melt of a coating material composed of, for example, hardened oil, wax etc., spraying the resulting oil suspension using a spraying device or a rotary disc and solidifying the droplets formed by spraying by cooling, so as to form solid encapsulated particles of the water-soluble vitamin within a coverage layer of the coating material (See, for example, "Raw Feed Composition for Fish Cultivation" described in the Japanese Patent Publication No. 13192/1975, "Feeds for Fish Cultivation" given in the Japanese Patent Application Kokai No. 205461/1983 and so on).
The second way consists of a so-called fluidized bed process which comprises the steps of forming a gaseous suspension of a particulate product of a water-soluble vitamin in a pneumatically fluidized layer by an airstream blown up from the bottom of a fluidizing apparatus and spraying a solution of a coating material, such as a hardened fatty oil, wax etc., in a volatile solvent into the fluidized layer as a mist or liquid droplets from the side or upper portion of the fluidized layer to effect coating of the vitamin particles and evaporate off the solvent to dry the coating layer, or similar procedures using a fluidizing apparatus (See, for example, "Process for Effecting Coating of Particulate Product of Vitamin" as given in the Japanese Patent Application Kokai No. 52221/1975).
As to the coating material to be employed for producing coated or encapsulated particulate preparation of vitamins, there have been disclosed numerous studies, such as for example, "Method for Stabilizing L-Ascorbic Acid and its Salts" with the use of hardened fatty oils, lecithin and glycerin fatty acid monoesters, as given in Japanese Patent Publication No. 16779/1981; "Feeds for Fish Cultivation" with the use of higher fatty acids, as disclosed in Japanese Patent Application Kokai No. 205461/1983; "Thiamin Preparation for Fish Cultivation" with the use of waxes, as disclosed in Japanese Patent Application Kokai No. 157020/1984 and so on.
The conventional coated vitamin C preparations for animal feeds have disadvantages, such as for example, insufficient coverage performance, low content of vitamin C in the preparation with the concomitant necessity of a large application rate, poor conservation of vitamin C activity, lower absorbability of vitamin C by organisms and so on.
On the other hand, there has been proposed a method for coating over the entire circumferential surface of each particle of a pulverous product of amino acids as a core material with a layer of a powdery product of a lipid having a melting point of at least 40.degree. C. as a coating material by causing the particles of the coating material to adhere uniformly onto the surface of particle of the core material (Japanese Patent Application Kokai No. 2554/1989). If this method is applied to effect coating of particles of a pulverous vitamin C product, no coated vitamin C preparation exhibiting a superior preservation of vitamic activity can be obtained.